On the Processing of "Extinguished" Stimuli in Unilateral Visual Neglect: An Approach Using Negative Priming

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Abstract
We report experiments examining the processing of "extinguished" stimuli in a patient showing visual extinction to double simultaneous stimulation. The experiments used a matching paradigm, designed so that extinguished stimuli cannot benefit from priming from non-extinguished stimuli presented simultaneously. The task involved matching for physical identity central targets in prime and probe displays, flanked by distractors. On "different" trials, distractors in primes could re-appear as targets in probe displays (the ignored repetition condition). Experiments 1 and 3 used normal subjects and established negative priming in the ignored repetition condition. Negative priming occurred both when stimuli in the prime and the probe displays were the same case and when they differed in case. Experiment 2 used a patient manifesting left-field neglect. Like control subjects, he showed negative priming from right-field distractors. In contrast, however, he showed positive priming from left-field distractors. Positive priming also occurred when distractors and targets differed in case (Experim ent 2b). Experiment 4 showed that the patient showed marked left-field extinction under conditions equivalent to those used in the matching task. The data indicate both that "extinguished" stimuli can be processed to activate internal representations and that inhibitory processes may not be applied unless conscious attention is involved.

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